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Tuesday, December 31, 2013

Beyond
unsupported assertions in H.G. Wells “The Outline of History,” geologists
have long argued that the Mediterranean Basin had completely dried. One important event, the Messinian salinity
crisis, had global impacts on biota, oceanography, and perhaps climate.In this study, Lugli et al. review the
sedimentology and stratigraphy of cores that penetrate the evaporite fills of
marginal canyons from Miocene (Messinian) strata in the Levant Basin, onshore
Israel.The results reveal an absence of
primary in situ evaporites; instead, the
cores include only clastic sulfate facies, deposited by subaqueous gravity
flows sourced from dismantled selenite rocks originally located eastward and
updip of the canyons. This association and the presence of the evaporite layers
at different elevations along the canyons are interpreted to be the result of
subaqueous mass-wasting phenomena, and that evaporites provide no evidence for marked
sea level drop during the salinity crisis. On the contrary, the widespread
presence of clastic evaporites is interpreted to suggest that a broad water body persisted through
the acme of the salinity crisis.

Thursday, December 19, 2013

In
December 19631, as Frankie Valli2 and the Four Seasons
enjoyed a very special night, Donald Campbell excited
JSP readers on percussion. Campbell’s study examined percussion marks,
surficial crescentric cracks, on quartz
grains from Cambrian and Cretaceous sandstones of central Texas. His results
suggested that percussion marks are diagnostic of eolian transport. Unlike that
special night (that ended much too soon), however, percussion marks are durable
and can persist for several episodes of sediment recycling. As such, they alone
are not indicative of deposition in an eolian environment.

1 The song, describing a romantic encounter, actually came
out in 1976, when it hit #1 in both the US and UK charts.A remix hit #14 in the US Billboard Hot 100
chart in 1994.But hopefully PaperClips
readers understand and appreciate the pop culture-savvy reference.

2 Editor’s note: Valli was actually not the lead singer on
this track, drummer Gerry Polci provided lead vocals.But by all accounts, Frankie was the leader
of the group.

Monday, December 16, 2013

Many dolomitized platform
carbonate successions are associated with evaporites, and many studies link
dolomite to reflux associated with hypersaline brines. In this paper, Rott and Qing describe petrographic
observations and geochemical data to explore the genesis of pervasive
matrix-replacive dolomite in a succession not associated with evaporites, the
Mississippian Alida Beds in the Williston Basin of Canada. Petrographic
observations and δ13C compositions suggest an initial dolomitizing
event driven by slightly evaporated seawater (but not enough for gypsum
saturation), although depleted δ18O values, elevated 87Sr/86Sr
ratios, and correlation of dolomite crystal sizes and δ18O values
are interpreted to represent variable recrystallization of this early
dolomite.This proposed conceptual model
may explain the occurrence of pervasive, matrix-replacive dolomite in the absence
of depositional evaporites, and may be appropriate for other regions and
hydrocarbon pools.

Thursday, December 12, 2013

Study of a suite of individual
grains can provide incredible information on depositional systems and tectonic
history. In this study, Vozárová et al. describe U-Pb (SHRIMP) detrital zircon ages from metasandstones
of six stratigraphic levels of the low-grade early Paleozoic Northern Gemeric
basement and its Carboniferous-Permian cover of the western Carpathians,
Central Europe. The results reveal: a) a
source from the Cadomian belt aged at between 550-700 Ma and from West African
craton provenances, of ca. 1.8-2.7 Ga, b) recycling of Precambrian detrital
zircon populations into the Carboniferous-Permian sedimentary basin fill, c) Variscan
(355 Ma) peak metamorphic deformation and closure of the early Paleozoic basin,
and d) extensional processes and high
exhumation and erosion rates of the Variscan collision belt.These dating results are interpreted to
uniquely record the complex sedimentary, metamorphic, and tectonic evolution of
this area.